The field of the present invention is the field of light modulator arrays.
Controlled modulation of light beams is a fundamental basis for a variety of useful devices. Examples include scanners, laser printers, and optical communication devices. Resolution in scanners and printers depends in large part on the ability to avoid interference from closely spaced modulated light beams. Similarly, bandwidth of optical communication devices is limited by interference between closely spaced modulator elements. Conventional light modulator arrays present one barrier to improved performance due to interference effects between adjacent elements in such arrays. Light modulator arrays are formed from electrooptical materials. Exemplary electrooptical materials include Lead Zircanate Titanate (PLZT), Barium Titanate, Strontium Barium Niobate, Gallium Arsenide, Potassium Tantalum Niobate, and materials having similar properties. Formation of conventional light modulator arrays typically involves the formation of electrodes on a wafer of electrooptical material. A pattern of electrodes defines discrete elements in the array. The surface on which the electrodes are formed becomes a light incident surface. The resultant geometry for the array has pairs of electrodes disposed on the light incident surface of the array. The electrodes are generally perpendicular to the incident light beam to be modulated.
Drawbacks arise in such a geometry. A first limitation arises from the planar geometry which limits penetration of the applied electric field into the electrooptic material to thereby reduce interaction length of the material and of the optical beam. A second limitation results from the fact that the applied modulation electric field to a given modulator increases the physical modulator dimension in the direction of the applied electric field as a result of piezoelectric modulation. This deformation introduces stress to neighboring modulators. Taking an example, PLZT light modulators can efficiently modulate large optical powers for optical wavelengths above 600 nm. However, PLZT modulator arrays have not found a large span of applications, due to limitations imposed by large applied voltages to achieve half wave modulation and because of the inter-pixel crosstalk resulting from strain birefringence.
Prior patents, including U.S. Pat. Nos. 5,198,920 and 5,260,719, have introduced packaging concepts that address either the interaction length or birefringence problem. No approaches have been put forward until now, to the best of our knowledge, that can fundamentally eliminate both limitations at once. In addition, the prior patents fail to address the basic issue of an array geometry that addresses these problems independently of a particular packaging approach. Instead, some particular packaging solutions have compensated for a problem inherent to the conventional planar array geometry.
Another limitation of previous device geometries has been their fabrication and packaging complexity leading to high cost modulator arrays. Many devices which use such arrays, e.g., laser printers and scanners, require low cost components since price competition is strong in the markets for such devices. Thus, there is a need for an improved light modulator array geometry.
Such needs are met or exceeded by the present invention. According to the invention, an improved linear light modulator array is formed with opposing electrodes that extend away from the optic surfaces of electrooptical material used to form the array. A uniform electric field is created across a modulator volume, generally perpendicular to light propagation within the modulator volume. The modulator volume of an element in the array is a function of electrode length, width and separation. Additional elements are defined by additional pairs of electrodes. Trenches that penetrate the electrooptical material are disposed between modulator elements. Preferably, the trenches penetrate the electrooptical material a distance that is approximately 10-15% of a distance separating opposing electrodes.
The invention includes a method for forming the array geometry of the invention. According to the method, electrooptical material into, is cut into strips. Cut sides of the strips are metallized, one at a time, with the opposite side temporarily affixed to a carrier. Aligned trenches are cut in the metallized strips and the electrooptical material to separate electrode pairs and define array elements.